1. Field of Invention
The invention relates to an electronic animal containment system. More particularly, the invention relates to an electronic animal containment system capable of determining whether an animal approaching the boundary wire is inside or outside the containment boundary.
2. Description of the Related Art
Electronic animal containment systems are commonly used to keep an animal within a prescribed boundary. The typical electronic animal containment system includes a wire loop antenna that bounds the containment area, a transmitter connected to the wire loop that generates a signal carried by the wire loop, and a receiver responsive to the signal that issues warnings and/or corrections when the animal approaches the wire loop boundary.
Conventional electronic animal containment systems lack the ability to discriminate between an animal approaching the wire loop boundary from inside the bounded area and an animal approaching the wire loop boundary from outside the bounded area. Thus, if an animal manages to escape the bounded area, it will receive a warning and/or a correction when the animal attempts to reenter the bounded area.
A previous attempt to avoid correcting an animal as it returns to the containment area is described in U.S. Pat. No. 4,745,882, entitled “Electronic Confinement and Communications Arrangement for Animals,” issued to Robert G. Yarnall, Sr., et al., on May 24, 1988 (“the '882 patent”). The '882 patent discloses the use of two boundary wires carrying distinct signals generated by two separate containment transmitters and a deactivation circuit that deactivates the containment transmitters when an animal escapes. By deactivating the containment transmitters, the animal can return to the containment area without receiving additional corrections. The advantages of the '882 patent are tempered by the required duplication of components and by the fact that reentry without correction requires deactivating the containment transmitters. When used with multiple animals, the escape of one animal deactivates the containment function with respect to both the escaped animal and the animals still within the bounded area.
U.S. Pat. No. 5,794,569, entitled “Apparatus and Method for Electronic Confinement of Animals,” issued to John Titus, et al., on Aug. 18, 1998 (“the '569 patent”) declares that there is “a need for an electronic animal control system which does not correct an animal trying to re-enter a confinement area.” U.S. Pat. No. 5,794,569, col. 1, ll. 39-41. In order to determine whether the animal is leaving or entering the confinement area, the Titus apparatus includes a unipolar polarity pulse at the end of the coded signal. Id. at col. 10, ll. 63-67. The portable unit effectively drops the negative portion of the coded signal during the decoding process. See Id. at col. 11, ll. 1-25. Thus, the polarity of the coded signal is determined by the presence or absence of the polarity pulse. Id. When the presence or absence of the polarity pulse is combined with information from a tilt switch array, the portable unit is capable of predicting whether the animal is inside or outside the confinement area. Id. at 67. The portable unit notifies the transmitter using a radio signal when the boundary signal is detected. Id. at col. 5, ll. 30-34. The notification signal includes information about whether the animal is inside or outside the confinement area. Id. at col. 11, ll. 62-67. The transmitter determines the appropriate correction and generates a coded signal for instructing the portable unit how to correct the animal. Id. at col. 5, l. 34 to col. 6, l. 3. If the animal has escaped the confinement area and is attempting reentry, the portable unit must notify the transmitter has cleared the outer zone around the perimeter wire. Id. at col. 12, ll. 1-7.